A. I. Savchuk

Magneto-optical Faraday rotation of semiconductor nanoparticles embedded in dielectric matrices

Faraday rotation has been studied for CdS, CdTe, and CdS:Mn semiconductor nanoparticles synthesized by colloidal chemistry methods. Additionally these materials were prepared in a form of semiconductor nanoparticles embedded in polyvinyl alcohol films. Transmission electron microscopy and atomic force microscopy analyses served as confirmation of nanocrystallinity and estimation of the average size of the nanoparticles. Spectral dependence of the Faraday rotation for the studied nanocrystals and nanocomposites is correlated with a blueshift of the absorption edge due to the confinement effect in zero-dimensional structures. Faraday rotation spectra and their temperature behavior in Mn-doped nanocrystals demonstrates peculiarities, which are associated with s, p-d exchange interaction between Mn²⁺ ions and band carriers in diluted magnetic semiconductor nanostructures.

Magnetic and magneto-optical properties of CdS:Mn quantum dots in PVA matrix

We have studied the magnetic and magneto-optical properties of CdS:Mn quantum dots in polyvinyl alcohol matrix synthesized by co-precipitation method. The size of quantum dots was estimated by means of absorption spectroscopy. The results of measurements of magnetic susceptibility as a function of temperature and spectral dependence of the Faraday rotation of CdS:Mn quantum dots / polyvinyl alcohol composites are presented. In this work magnetic susceptibility was investigated by Faradays method at the temperatures of (78-300) K in magnetic fields of (0.05-0.8) T. The inverse magnetic susceptibility as a function of temperature follows a Curie Weiss law. Formation of ferromagnetic coupling between magnetic ions is supposed. Magneto-optical Faraday rotation has been investigated in the wavelength region (400-700) nm at temperature 300 K in a magnetic field up to 5 T. Sign of the Verdet constant is found to be negative.

Interaction of human serum albumin with CdTe quantum dots probed by optical spectroscopy methods

In this work, colloidal CdTe nanoparticles were synthesized by using thioglycolic acid (TGA) as passivator. In the absorption spectra of the colloidal CdTe nanoparticles exciton band was found to be shifted to higher photon energy as compared with bulk crystals due to quantum confinement effect. It was shown that addition of human serum albumin (HSA) to colloidal CdTe nanoparticles led to a gradual decrease of absorption and broadening of exciton structure. However, energy position of the exciton band in this case remains not shifted. In photoluminescence spectra of solution CdTe quantum dots and HSA so-called quenching effect has been observed. The quenching of HSA fluorescence intensity by semiconductor nanoparticles was analysed in framework of the formation of quantum dots-HSA protein complex.

Optical and magneto-optical diagnostics of polymer/nanoparticles colloidal solutions and composites

In this work we report on peculiarities of technique for correct measurements of optical transmittance, optical density and Faraday rotation spectra of colloidal semiconductor nanoparticles and nanocomposites. As an example we have used CdS:Mn nanoparticles embedded in polyvinylalcohol (PVA) matrix. With the decrease of the size of CdS:Mn nanoparticles, the absorption exciton band was shifted to shorter wavelengths as a result of quantum confinement effect. In order to observe clearly this shift we have used several samples with the same average nanoparticle size, but with different sample thicknesses. It was made analysis of the obtained data on optical spectra for nanocomposites with comparison for bulk semiconductor materials. Similar methodology was applied for magneto-optical spectra of colloidal solutions and nanocomposites.

Growth and investigation of ZnHgMnTe crystals for magnetic field sensors

AbstractSingle crystals of Zn Hg Mn Te grown by a modified Bridgman method have been investigated by means of optical 1yxyyx y spectroscopy and the Faraday rotation techniques. It has been found that structural, optical and magnetooptical characteristics of thestudied quaternary semimagnetic semiconductor with xs0.5, ys0.4 have good prospects for applications as sensing elements inmagnetic field sensors. An advantage of the material, as compared with Cd Mn Te, is its better performance in the range of laser 1yxx wavelengths above 800 nm, for which cheap and low-noise laser diodes are available.q2000 Elsevier Science S.A. All rights reserved. Keywords: Faraday rotation; Semimagnetic semiconductor; Crystal; Growth; Energy bandgap; Magnetic field sensor 1. IntroductionThe magnetooptical Faraday effect provides fertileground for different applications of magnetic materials,including a variety of magnetic sensors. Recently, semi-magnetic semiconductors have been added as promisingcandidates for such applications owing to their giant Fara-day rotation. Among the semimagnetic semiconductors,solid solutions of Cd Mn Te are the most extensively

Two-dimensional materials as inorganic analogues of graphene: methods of preparation, optical properties, and applications

Two-dimensional (2D) materials such as GaSe, InSe, and WSe2 in form of bulk crystal and few-layer sheets have been prepared by mechanical exfoliation method. Atomic force microscopy (AFM) analysis was used for the study of surface morphology and estimation of thicknesses of the exfoliated thin semiconductor layers. Optical absorption and magneto-optical Faraday rotation spectra of 2D materials at different temperatures have been studied. In spectral region near long-wavelength absorption edge for all the studied layered crystals at low temperatures the exciton series have been observed. It was shown that in GaSe and InSe crystals these series consist of three lines, whereas in WSe2 two exciton lines were revealed. The observed exciton series were interpreted in framework of 3D exciton model. In the absorption spectra of GaSe and InSe crystals at higher photon energies than band gap Eg additional exciton structure also was observed. In case of thin exfoliated WSe2 flakes with thickness less than 80 nm shift of ground exciton band to shorter wavelengths has been revealed, which is associated with quantum size effect. Faraday rotation spectra of the 2D crystals have been confirme INTRODd dominant role of excitons near absorption edge.

Zinc oxide based diluted magnetic semiconductor nanoparticles: Synthesis by laser ablation in liquids, microstructural and optical properties

Nanoparticles of ZnO and ZnO doped with transition metals (Mn, Co) were synthesized by laser ablation in liquid medium. Scanning electron microscopy (SEM) showed formation of nanostructures with different shapes. Atomic force microscopy (AFM) gives information about surface morphology of the formed nanostructures. Absorption edge of ZnO, ZnO:Mn and ZnO:Co colloidal nanoparticles exhibits blue shift due to confinement effect. In photoluminescence spectra three peaks are attributed to the band-edge transitions and defect states. The Faraday rotation in ZnO:Mn nanoparticles gives evidence for paramagnetic behavior at room temperature.

Surface morphology, optical properties and sensing characteristics of ZnMeO ( Me - Mn, Co, Ni ) thin films

Zn1-xMexO (Me- Mn, Co, Ni) thin films were grown by pulsed laser deposition and rf magnetron sputtering methods. The composite targets were formed by mixing and pressing of ZnO, Mn3O4, CoO and NiO powders. The thin films were deposited on sapphire, quartz and glass substrates. The structure study confirms the formation of the hexagonal wurtzite ZnO without any secondary phase in transition metal (Mn, Co, Ni) - doped samples. The surface morphology of the thin films was studied using atomic force microscopy (AFM). Different surface morphology AFM images were obtained depending on the film composition and growth conditions. Optical absorption spectra suggest of substitution Zn2+ ions in ZnO lattice by transition metal atoms. The shift of the absorption edge due to decrease the energy band gap with increasing cobalt content and complex dependence of the energy band gap on content of nickel was observed in optical absorption spectra of the studied films.

Optical and magneto-optical properties of PbFeI2 nanoparticles

Nanocrystals of Pb1-xFexI2 with x up to 0.05 embedded in transparent polymer matrix have been studied by optical absorption, photoluminescence and electron paramagneric resonance. The composite nanostructures containing the semimagnetic semiconductor nanocrystals of Pb1-xFexI2 have been prepared by cooling to the room temperature of boiling saturated aqueous solution. The absorption spectra of nanoparticles exhibit blue shift due to quantum confinement effect. For colloidal solution of nanocrystals and nanostructures incorporated in polymer matrix based on polyvinylalcohol exciton structures of absorption spectra was observed. In photoluminescence spectra of nanoparticles two main peaks were revealed, which are attributed to the band-edge transmission and defects states. The substitutional incorporation of iron ions at lead sites is reflected in EPR studies. Isolated as well as interacting Fe3+ ions are observed in EPR spectra of Pb1-xFexI2 nanocrystals.

Optical and magneto-optical properties of PbFeI 2 nanoparticles

Nanocrystals of Pb1-xFexI2 with x up to 0.05 embedded in transparent polymer matrix have been studied by optical absorption, photoluminescence and electron paramagneric resonance. The composite nanostructures containing the semimagnetic semiconductor nanocrystals of Pb1-xFexI2 have been prepared by cooling to the room temperature of boiling saturated aqueous solution. The absorption spectra of nanoparticles exhibit blue shift due to quantum confinement effect. For colloidal solution of nanocrystals and nanostructures incorporated in polymer matrix based on polyvinylalcohol exciton structures of absorption spectra was observed. In photoluminescence spectra of nanoparticles two main peaks were revealed, which are attributed to the band-edge transmission and defects states. The substitutional incorporation of iron ions at lead sites is reflected in EPR studies. Isolated as well as interacting Fe3+ ions are observed in EPR spectra of Pb1-xFexI2 nanocrystals.